Hope I'm not too late. DON'T DO IT!! We all know with absolute certainty that the Canon 14-24mm f/2.8L IS will be available in just a matter of days, since it's a typical stealth Canon launch and retailers already have stock in their back rooms. When the new lens comes out, it will instantly make all the pictures you'll ever take with the 16-35mm f/2.8L II turn into absolute crap. So, by all means, don't buy that lens...
Okay, seriously, it's a very good lens - provided you're sure it's the focal length you want/need, and you need f/2.8. Hopefully, you're using it on a FF body - else, there are many better options to consider. On FF, stopped down to f/8 or so, the 17-40mm f/4L delivers IQ that's on par with the 16-35mm II, and the 17-40mm is substantially less expensive, and uses more common 77mm filters instead of the 82mm variety. Don't downplay that too much - true, a CPL will result in uneven polarization of skies wider than 24mm (on FF), but if you need the lens to be weather-sealed, that means a UV/celar filter is necessary. I'd really like a screw-in 10-stop ND for my 16-35mm II (and my TS-E 24mm II), but there just isn't one.
Enjoy the lens!